The invention relates to apparatus for converting a measurement signal V.sub.R(i), which is disturbed at least occasionally by a disturbance function into an undisturbed signal V.sub.R(o) by the use of a filter having variable filter parameters.
When the speed of a vehicle wheel, is measured for the purpose of brake-pressure control (ABS), for example, there is frequently impressed on the measurement signal V.sub.R(i) a disturbance signal of one or more specific frequencies which can distort the signals to be evaluated (e.g., the wheel-speed signal itself or its derivatives).
It is known quite generally that disturbance signals can be eliminated by filtering. However, the frequencies of the disturbances often are not known and, moreover, such frequencies are variable as a function of the given influences. So-called adaptive digital filters therefore lend themselves to such filtering; however, they must be adjusted so that only the disturbance signal is filtered out.